The present invention relates generally to a twist tie fastener. More particularly, the present invention relates to a polymeric twist tie fastener that exhibits superior strength and flexibility characteristics.
Twist ties are used for various fastening and closing purposes. Typically, twist ties are used to seal a package having an open end, such as a bag. To seal the package, packaging material that is adjacent to the open end is gathered. The twist tie is wrapped around the gathered package material until end portions of the twist tie are adjacent to each other. The end portions are then twisted relative to the remainder of the twist tie to fasten the twist tie onto the package.
Twist ties typically include a wire that is enclosed in a paper or plastic wing. Twist ties that include the paper or plastic enclosed wire are subsequently referred to as wire twist ties. Wire twist ties have many advantageous properties that have led to widespread use of wire twist ties. For example, wire twist ties are readily applied using either manual or high speed mechanical operations. In addition, multiple fastening and unfastening cycles do not significantly affect the fastening capability of the wire twist ties. Wire twist ties are also functional over a wide range of temperatures without a significant reduction in fastening capability.
There are many food packaging applications where wire twist ties play an important role because wire twist ties enable consumers to quickly access and reseal a product numerous times. One disadvantage of existing wire twist ties is that consumers desire food packaging that enables heating of the food in its original packaging, such as in a microwave oven. Existing wire twist ties, however, are not suitable for use in a microwave because the wire twist ties generally cause undesirable arcing when the twist tie is subjected to microwave radiation at an intensity that is found in microwave ovens.
Another disadvantage of existing wire twist ties concerns conventional food distribution. When food is commercially packaged for distribution to the public, it is desirable to insure that the food is free from foreign object contamination. Therefore, commercially packaged food is typically inspected after the food is packaged. A common method of inspecting food products is with metal detectors. However, existing wire twist ties preclude the use of metal detectors.
To overcome these difficulties, a variety of non-metallic closures, such as polymeric closures, have been developed. Polymeric twist ties are an example of the polymeric closures. There have been numerous attempts to develop a polymeric twist tie that exhibits desirable toughness and flexibility characteristics while also being easily fastenable and unfastenable over numerous cycles. One such entirely polymeric twist tie is disclosed in Stolk et al., U.S. Pat. No. 4,797,313. Stolk et al. disclose using polymeric materials that provide a yield stress of less than 9,000 psi and preferably between 2,000 psi and 4,000 psi. Stolk et al. indicate that a yield stress of less than 9,000 psi is necessary so that the polymeric materials exhibit a desired glass/rubber transition behavior.
There have been numerous other attempts to provide an entirely polymeric closure device. For example, Thomas, U.S. Pat. No. 3,535,746; Moon, U.S. Pat. No. 3,604,066; and Hoard, U.S. Pat. No. 3.945,086, disclose polymeric closure devices. However, none of these polymeric closure devices are believed suitable for substitution in place of wire twist ties in machinery that presently handles high speed mechanical packaging with wire twist ties.